This invention relates to mine roof support systems and more particularly, it concerns improvements in mine roof support systems of the type including a plurality of telescopically interconnected support units arranged to provide transverse parallel lines of roof support over a work area and capable of being self-advanced during mining operations.
As exemplified in U.S. Pat. No. 2,795,935-Fitzgerald, No. 2,795,936-Blower et al and No. 4,143,991-Stafford, mine roof support systems are known to be available for continuous mining operations in which a plurality of inverted U-shaped units are capable of self-advancement with mining operations to protect the working area between the mining face and the area under a roof which has been permanently reinforced such as by timber and/or roof bolting. In contradistinction to well-known roof jacks used in long-wall mining operations, the units of the systems disclosed in these patents are arranged in tandem and each include a transverse beam or truss supported at opposite ends by a pair of extensible props so that the units lie perpendicular to the direction of advance rather than parallel to the direction of advance as in the case of long-wall jacks. In a manner common to most self-advancing roof support systems used in mining operations, these systems employ telescopic struts between successive units so that as one unit is retracted away from the mine roof, it may be pushed or pulled by extension or contraction of the struts reacting with another unit which is fixed as a result of it being forcibly retained between the mine floor and the mine roof.
To facilitate an understanding of component orientation in mine roof support systems of the type under discussion, the term "unit plane" will be used hereinafter to designate a plane containing the central axes of the transverse roof engaging beam and of the extensible props supporting opposite ends of the beam for each inverted U-shaped unit of the system. In light of basic system geometry, therefore, each unit plane will be generally vertical and perpendicular to the direction of system advance with mining operations as well as generally perpendicular to the struts extending between and interconnecting successive units of the system. Also, it will be appreciated that maximum roof support capability will be obtained when the unit plane and the axes of both unit props in that plane are truely vertical irrespective of undulations in the mine floor or roof, relative inclination of the mine floor or roof in the unit plane and the like.
Maximum roof supporting capacity has been achieved in such systems by appropriate pivotal interconnection of the props with the beams in each unit as well as of the struts with the props between successive units. To retain each unit in an essentially erect condition when the beam thereof is retracted away from the roof for longitudinal advance of the unit, however, provision must be made for stabilizing the pivotal connection of components. For example, the props and beam of each unit must be restored and retained in an essentially perpendicular relationship and also the connection of the longitudinal struts with the props of a retracted unit must be maintained near perpendicular to assure that the unit plane of a unit being advanced relative to another unit will remain essentially vertical while at the same time accommodate undulations in the mine floor. In the past, these requirements have involved design compromise between structural integrity and ruggedness required by the mining environment on the one hand and, on the other hand, a kind of simplicity important to such factors as cost and weight reduction as well as efficient and safe mining conditions which necessitate a minimum of interference by the support system with maneuverability of mining equipment and personnel.